The invention relates to refiners for refining a fibrous material, such as wood or the like, comprising a stator and a rotor having a conical portion. More particularly, the invention relates to a blade element for a conical portion of a stator of a refiner, which blade element comprises a feed end, a discharge end, and a refining surface which comprises a feed zone at the feed end of the blade element.
Refiners are used for processing a fibrous material, such as wood or the like, to produce different fibre pulps. A typical refiner comprises oppositely situated stator and rotor, the stator being fixed and the rotor being arranged to rotate about a shaft such that the rotor rotates or turns relative to the stator. The stator and the rotor comprise refining surfaces typically consisting of blade bars and blade grooves therebetween. The material to be refined is fed into a blade gap provided between the stator and the rotor, whereby the refining surfaces of the stator and the rotor refine the material when the rotor rotates relative to the stator.
There are basically two different kinds of refiners comprising a conical portion. A first kind of refiner comprising a conical portion is provided with both a flat portion and a conical portion, whereby the material is first refined in the flat portion of the refiner and thereafter in the conical portion of the refiner. This kind of refiner comprising both the flat portion and the conical portion is typically used for refining a material having a high consistency. A second kind of refiner comprising a conical portion only comprises a conical portion. This kind of refiner only comprising the conical portion is typically used for refining a material having a low consistency. In the conical portion of the refiner, an end of the conical portion having a smaller diameter provides the feed end of the conical portion, where the material to be refined is fed into the blade gap of the conical portion, and an end of the conical portion having a larger diameter provides a discharge end of the conical portion, where the material already refined is discharged out of the blade gap of the conical portion.
In the refiners having the conical portion, the feed of the material to the blade gap in the conical portion is a limiting factor when considering the production capacity of the refiner. This is the case in both refiner types mentioned above. In the refiners comprising both a flat portion and a conical portion, a transition from the flat portion to the conical portion causes a large open volume where a flow of the material to be refined may stop. In the refiners only comprising the conical portion, the material to be refined is fed into the conical blade gap from a large open volume, whereby no specific pressure is provided to promote the flow of the material into the blade gap. At the same time there typically also occurs a change in the direction of the flow of the material when the material is fed from the large open volume into the blade gap, the change in the direction also hindering the flow of the material to the blade gap of the conical portion.
In order to improve the feed of the material into the conical portion of the refiner, some modifications in the structure of the refining surfaces of the conical stator and the conical rotor have been introduced. When considering the refining surface of the conical rotor, these modifications include increasing the height of the blade bars in the feed zone of the refining surface of the conical rotor. When considering the refining surface of the conical stator, these modifications include providing the feed zone of the refining surface of the stator with shoulder-like guide elements intended for guiding the flow of the material forward from the feed zone. In the refiners only comprising the conical portion, these shoulder-like guide elements typically have the form of a bar while in the refiners comprising both a flat portion and a conical portion these shoulder-like guide elements typically have the form of a triangle. EP publication 0 958 057 B1 also discloses a solution for a refiner comprising both a flat portion and a conical portion. This solution comprises a kind of wings at the feed zone of the refining surface of the conical rotor for throwing the material to be refined toward the refining surface of the conical stator, the feed zone of the refining surface of the conical stator comprising shoulder-like guide elements having the form of triangle to guide the flow of the material forward into the conical blade gap between the stator and the rotor.